Class 2 (2nd Engineer) MEKM 📅 Oct 2022

Exam Question

(a) Explain the term fuel ignition quality and indicate how a fuel's chemical structure influences its value.

(b) State, with reasons, the possible consequences of operating an engine on a fuel with a lower ignition quality than that for which it is timed.

(ii) State what checks can be carried out in order to determine that the engine is operating correctly

Reference Answer

(a) Fuel Ignition Quality and Chemical Structure
Fuel ignition quality is the ability of a fuel to ignite spontaneously when injected into the compressed air charge in an engine cylinder. This property is measured by the cetane number . A higher cetane number indicates a shorter ignition delay and better ignition quality.
A fuel's chemical structure significantly influences its ignition quality. The cetane number is determined by comparing the fuel's ignition performance to two primary reference fuels:
n-hexadecane (cetane) : A straight-chain paraffin with very good ignition quality and a cetane number of 100.

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